A conventional communication receiver (e.g., a selective call receiver or pager) normally receives and decodes a transmitted signal in a known way. The contemporary receiver typically receives a modulated carrier signal and converts the carrier signal to an intermediate frequency signal using at least one mixing signal that may be provided from a fixed local oscillator. Subsequently, a demodulating stage substantially recovers an information signal. The recovered information signal may be provided to a decoder to extract encoded data information (e.g., pager address and other control information, as well as optional message data), and/or may be provided to an audio circuit to present an audible alert or other audible signal to a user of the communication receiver.
The recovered information signal typically may include noise and distortion due to a number of sources. One particularly regrettable source of distortion may result from the unmodulated carrier signal being relatively unsynchronized with the at least one mixing signal. Due to variability of a transmitted carrier signal relative to a specified tolerance range at the receiver, further aggravated by variability of the at least one mixing signal from the fixed local oscillator, the receiver demodulating circuits may provide a substantially distorted recovered signal.
Moreover, in conventional communication systems the user of the receiver may roam from one transmitter signal to another (e.g., in simulcast paging systems), therefore providing diverse carrier signals to the receiver (i.e., usually within a specified acceptable operating range). Consequently, the received modulated carrier signal mixes with the at least one mixing signal and demodulates to a recovered information signal that may be substantially distorted.
The unfortunate distortion may be due to the recovered information signal dynamic range being substantially skewed with respect to an acceptable operating range for the demodulating circuits. That is, the recovered information signal excursions may traverse beyond an acceptable operating range for the demodulating circuits. Typically, an acceptable operating range may comprise a linear operating region, and beyond the acceptable operating range may comprise a nonlinear operating region. Therefore, the recovered information signal may regrettably include less than optimum excursions (i.e., distortion).
Additionally, a signal-to-noise ratio (S/N) for the receiver may be seriously degraded by the reduced effective dynamic range of the recovered signal. Since the recovered signal excursions may be substantially limited at an operating range boundary, the overall recovered signal dynamic range is reduced, and consequently the signal-to-noise ratio for the recovered signal is degraded. Therefore, the unfortunate lack of synchronization between a transmitted carrier signal and the at least one mixing signal at the receiver may detrimentally affect the signal-to-noise ratio for the receiver. Further, the subsequent decoding of a recovered data signal may be potentially "falsed" by noise signals, possibly missing a critical transmitted communication (e.g., a system control information, or a vital message for the user of the receiver).
Therefore, it is regrettable that no known communication receiver is capable of monitoring the recovered signal excursions and adaptively maintaining the recovered signal excursions to within an acceptable operating range by substantially resynchronizing the at least one mixing signal to the varying transmitted carrier signal.